The main flaw I see with your reasoning: Completion of part 1 does not unlock flying.
However, for the sake of argument, lets say that a player buys the game, completes part 1, then unsubs until part 2. That's still the box price plus one month. Then an additional month when he/she subs for part 2. Then again for part 3? 4? 5? Each time a month of sub is tacked on without actually knowing when the final completion will be available.
A person who stays subbed the entire time is giving Blizzard even more money because of situations like right now. Pathfinder part 1 could be finished in a month, but 7.1 does not have pathfinder part 2(that we know of, anyway). Any further gaps between stages increases Blizzard profits from players like these.
Now, a person who waits until the final completion is fully visible will not only be able to finish all objectives in one go(if that's how they want to play), but will do so more quickly due to any catch-up mechanics, or even just due to the availability of higher level gear. But even then such a player will be subject to time-gated completion of things like the Order Hall campaign, allowing Blizzard to directly set a minimum time required to unlock flight. Lets say, for the sake of argument, that Part 1 can be completed in a month, as you say. If ANY combination of requirements for part 2 onward pushes the time investment past the 1 month mark, it's a clear indication of Blizzard using the carrot of flying to artificially inflate sub profits.
Because that's what you're doing. I'm sorry if you don't recognize that. Every time I've attempted to clarify my points, they've been subject to straw man responses, or completely misinterpreted.
The problem here is that you're looking at all the various arguments and responses I've made in the past, taken them out of context, then mashed them all together. What you need to understand is that many of these arguments and responses are completely separate and compartmentalized, and were never meant as some kind of unified approach. I'm arguing or responding to each point on a case by case basis, within their own context.
I don't have the willpower to repeatedly break each individual argument down into its proper context just for your own personal clarification. I've explained each point multiple times, and if you want to consider them contradictory or false, or flawed, then I can't stop you. As I've said, at this point it's just easier to agree to disagree.
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Is your desire to see people running around on the ground more important or valuable than my desire to enjoy things from the air? This is why I've suggested in the past that the disparity between the power of flying and ground mounts should be addressed. Choosing between flying or ground should be a REAL choice, with pros and cons to each. That way people like you can enjoy the ground while people like me get the air. Neither side is wrong. Both sides win.
A person doesn't have to play vanilla to have experienced the lack of flight. Outside of Cata, every expansion's leveling content was no-flying. Many expansions had no-fly islands or instances used as level-cap content. Not trying to imply anything with this, just pointing out that playing in vanilla isn't the only place to experience a lack of flying.
I personally like the idea of activating your flying mount having charges which slowly recover only while you're on the ground. If you activate them too often(such as with the "helicoptor" behavior), you'll be out of charges quickly. But for longer travel it's not an issue. This also seems like it would be the easiest to implement without disrupting Blizzard's ground design hardly at all.